1. Field of the Invention
The present invention relates to a process of solvent extraction of copper, more particularly to a process for efficient separation/recovery of copper involving selective extraction of the copper ion with the aid of an organic extractant from an aqueous chloride solution containing copper and one or more concomitant elements, discharged from an extractive metallurgy of non-ferrous metals or the like, and subsequent stripping, and also to a process of solvent extraction which can keep a high extraction yield of copper even when an extractant discharged from the stripping step is recycled.
2. Description of the Prior Art
Techniques for separation of copper from various concomitant elements are important challenges for an extractive metallurgy of non-ferrous metals, and treatment of copper-containing by-products from an extractive metallurgy of steel and metal-containing wastes, in order to improve yield and quality of copper and purity of iron, among others. One of the commonly used processes involves oxidation of iron and removal of the resulting precipitates, when copper, iron or the like are concomitantly present in a solution. However, the precipitate of iron hydroxide is generally low in purity, because of high moisture content and presence of one or more concomitant elements in addition to copper. Therefore, the precipitate is discarded in many cases, because of the limited applicable areas. As a result, coprecipitated copper is also discarded, leading to copper loss.
The effective solutions to these problems is a process of solvent extraction with an organic solvent as an extractant capable of concentrating the element present in a solution at a low concentration and separating the element from other elements on an industrial scale.
The representative solvent extraction processes for separating copper from iron include the followings.
One process is extraction of copper with an acid extractant (e.g., LIX64™) to treat a leach liquor from leaching of copper oxide ore partly containing a copper sulfide mineral with a sulfuric acid solution. Another process proposed so far is extraction of the copper ion with an extractant (e.g., LIX54™) to treat a leach liquor containing ammine from treatment of wastes of automobiles, home electric/electronic appliances or the like (disclosed by, e.g., JP-A 06-240373 (Pages 1 and 2)).
Extraction with an acid extractant generally needs a neutralizing agent, e.g., sodium hydroxide or ammonia, to keep the solution at pH 1.5 to 2.5, because the solution pH level decreases as copper is extracted. This causes problems of an accumulated neutralizing agent component in the leach liquor. Moreover, stripping of copper from an organic solvent discharged from an extraction step should be carried out in a strongly acidic region. Therefore, extraction and stripping of a leach liquor in which copper, iron or the like is leached in a strongly acidic region involve problems of massive acid and alkali consumption.
On the other hand, a solvating extractant, e.g., tributyl phosphate (TBP) or trioctyl phosphine oxide (TOPO), which has been used for separation of the iron ion, needs little acid or alkali in extraction and stripping for an aqueous chloride solution, because it can extract a metallic ion irrespective of solution pH level. However, a solvating extractant little works for extraction of the cupric ion. Therefore, solvent extraction applied to an aqueous chloride solution containing the cupric, ferrous and ferric ions with a solvating extractant can separate copper and iron from each other by extracting the ferric ion into the extract while leaving the cupric ion in the raffinate. However, the ferrous ion, when present, makes iron extraction unstable and should be oxidized beforehand into the ferric ion.
A process for extracting the cuprous ion with a solvating extractant is proposed to separate/recover copper from leach product liquor concomitantly containing nickel and cobalt discharged a chlorine-aided leaching, where the copper ion is reduced to the monovalent state prior to extraction (disclosed by, e.g., JP-A 08-176693 (Page 2)). This can separate the cuprous ion from nickel and cobalt by extraction. However, this document is silent on separation of copper from iron, when the latter is present in the liquor.
Recently, electrowinning of copper from an aqueous chloride solution has been attracting attention for hydrometallurgical process of a copper sulfide mineral. This is because the cuprous ion can be stably present in an aqueous chloride solution, unlike in a sulfuric acid solution. Therefore, electrolysis of a feed solution containing the cuprous ion brings an effect of halving power consumption from that for normal electrolysis of the cupric ion. An electrolysis feed is preferably an aqueous solution containing the cuprous chloride ion, but free of impurity elements, e.g., iron.
Moreover, a usual extraction process by TBP for an aqueous chloride solution concomitantly containing the silver ion needs an additional step of separating copper and silver from each other, because the silver ion cannot be extracted by TBP, as is the case with the cupric ion. Separation of silver and copper present in an aqueous chloride solution from each other is not easy, because of their chemical properties, and is generally carried out by an amalgam process with mercury. This causes problems related to environmental protection and economic efficiency, resulting from massive use of mercury. Another process removes silver in the form of precipitate by neutralization and sulfidation. This, however, also precipitates copper to deteriorate copper separation efficiency.
As discussed above, it is difficult to selectively separate copper from iron present in an aqueous chloride solution by extraction with an acid extractant without massively consuming an acid and alkali. Use of a solvating extractant, on the other hand, also involves problems, e.g., massive energy consumption, when electrowinning or the like is adopted to recover copper and iron by reduction from the respective iron and copper solutions as the extraction product liquors, the former containing the cupric ion while the latter ferric ion, even when a solvating extractant is used.
Under these circumstances, there are demands for solvent extraction processes which treat an aqueous chloride solution containing one or more elements in addition to copper by extraction with an organic extractant and subsequent stripping to separate/recover copper from the concomitant elements efficiently on an industrial scale, and also for processes which efficiently separate the copper and silver ions from each other.
In this specification, oxidation-reduction potential is that at 20° C., based on an Ag/AgCl electrode.